Electromagnetic constant velocity actuator



QlU-LZ $E'RRCH March 30, 1965 L. H. FULTON ETAL 7 ELECTROMAGNETIC CONSTANT VELOCITY ACTUATOR 2 SheetsSheet 1 Filed May 1, 1962 .f/larrieAx/s a; Mar/0M I NVEN'TOR) [AA/600M b5 fi/z mv a 4/ BY 510M450. 7/1 Tau March 30, 1965 H. FULTON ETAL 3,176,170

ELECTROMAGNETIC CONSTANT VELOCITY ACTUATOR Filed May 1, 1962 2 Sheets-Sheet 2 l I 4 I 1 F I Evan/K5 01/ 012 013 014 of; 0.14 017 d5 d9 [0 27/374!!! ran/1150 M0455 Mayra Array Er United States Patent 3,176,170 ELECTROMAGNETIC CONSTANT VELOCITY ACTUATOR Langdon H. Fulton, Wynnewood, Pa., and Thomas D.

Tilton, Lawrenceville, N.J., assignors to Radio Corporation of America, a corporation of Delaware Filed May 1, 1962, Ser. No. 191,587 9 Claims. (Cl. 310-12) The present invention relates generally to improved constant velocity actuators, and particularly to improved electrodynamic constant velocity actuators and also to combinations of such actuators with shutters of the focal plane type providing accurate timing and acceleration and deceleration of the shutter with an intervening interval of substantially constant velocity shutter travel.

The principal object of the present invention is to provide a novel electrically driven actuator providing substantially constant velocity actuation.

Another object of the present invention is to provide a novel reciprocating actuator which is capable of movement in either direction of travel.

A further object of the present invention is to provide a novel actuator, the movement of which is, in part, controlled by forces resulting from the generation of eddy currents throughout at least a portion of its shutter actuating-m eAA'vhiIu- /Still another object of the present invention is to provide a novel electrodynamic actuator having a driving coil, the turns of which are distributed in a manner to cause acceleration, followed by movement at a substantially constant velocity during a desired period.

A still further object of the invention is to provide a novel electrodynamic actuator having a driving coil, the winding turns of which are distributed in a manner to provide initial acceleration in both the forward and reverse direction of travel.

A still further object of the present invention is to provide a novel reciprocating shutter and a shutter actuator which is compatible with a high vacuum space environment and which, because of its low moving mass and reciprocating motion, produces a minimum net disturbance to the attitude and spin velocity of a space vehicle in which it may be used.

In accordance with the present invention, generally speaking, motion is imparted to a mechanically movable member by an actuator having a single, continuous distributed winding substantially coextensive with the range of significant movement of the actuator, the turns of the Winding being concentrated at least at one end of the winding with a less concentrated uniformly distributed portion of the winding successively adjacent the concentrated turn. Each concentration of the winding turns causes acceleration of the actuator during a brief accelerating period. Therefore, the actuator is or may be double acting having an essentially identical motion pattern in opposite directions on alternate strokes. An electrically conductive member having the form of an annular shell and being substantially coextensive with the uniformly distributed Winding portion produces an eddy current induced retarding force of magnitude proportional to, and direction opposite to the actuator velocity, which tends to counterbalance the driving force of the coil causing the velocity to become uniform at a desired value for imparting constant velocity motion to the mechanically movable member. By way of example, the novel actuator of this invention may be employed to impart movement to a focal plane shutter as the mechanically movable member mentioned above. The uniform velocity will provide uniform exposure and can have a value needed for a desired exposure time.

3,176,170 Patented Mar. 30, 1965 Other objects and advantages of the present invention, in addition to those stated above, will become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specification in connection with the accompanying drawing in which:

FIGURE 1 is a perspective view, more or less diagrammatic, of a camera having a shutter driven by an actuator of the present invention;

FIGURE 2 is a view in longitudinal section of the actuator housing of FIGURE 1, the section being taken on line 2-2 as viewed in the direction of the arrows;

FIGURE 3 is a view in vertical section taken on the line 3-3 of FIGURE 2 as viewed in the direction of the arrows;

FIGURE 4 is a fragmentary view to an enlarged scale of a portion of the coil structure shown in FIGURE 2 of the drawing; and

FIGURE 5 is a curve, including values by Way of example, of the stroke velocity curve of the movable member of the actuator of FIGURE 1 of the drawing.

The combined shutter and constant velocity actuator of this invention as shown by FIGURE 1 of the accompanying drawing, are embodied in a camera having a lens system 12 and a television camera tube 14. The actuator 16 will be described more in detail in connection with FIGURES 2, 3 and 4 of the drawing. The actuator 16 and the shutter 18 are mechanically interconnected by a driving rod 20 in the illustrative example. The driving rod 20 may be connected to any device to be driven. The shutter 18 comprises a shutter plate 23 having an exposure slit 25 and is supported and guided by a stationary aperture plate 26 having an aperture 28. The aperature plate 26 is supported in any suitable manner (not shown) by a stationary part of the camera 10. The aperture plate 26 has grooves 29 and 30 in which the shutter plate 23 slides.

The parts so far described will usually be mounted in a light tight camera case (not shown) admitting light only through the lens system 12. This case may be completely sealed when the camera is used in air-borne, or space-borne vehicles. Obviously the shutter exposure slit may cooperate with any image receiving area. For example, a photographic film or plate may be exposed by the shutter and actuator of the invention rather than the face of the camera tube 14. Also, it will be understood that the lens system 12, shown as a single lens for convenience of description, may be any form of imaging optics designed to image any scene or object located at any viewing distance from the camera on the face of the camera tube 14.

The actuator 16 comprises a magnetizable cylindrical member 35 (FIGURE 2), a magnetizable cap piece 38, a permanent magnet 39 and a magnetizable pole piece 41. The cylindrical member 35 had a restricted opening 43 at one end which together with pole piece 41 defines a cylindrical air gap across which flux produced by the permanent magnet 39 is concentrated. The magnet 39 may be made of Alnico V the composition of which is substantially aluminum 8%, nickel 14%, cobalt 24%, copper 3% and the remainder iron.

The movable coil structure is a self-supporting plastic thin walled cylinder 44 in which the coil 45 is embedded. This cylinder may be molded of a rigid organic resin containing reinforcing glass filaments, so that it presents smooth interior and exterior surfaces. The molded selfsupporting coil structure has minimum mass and maximum mechanical strength. The inside diameter is such that it slides freely on the exterior surface of the magnet 39 and the pole piece 41 and the outside diameter permits it to be received in the restricted opening 43 substantially without friction. The coil 45 as shown in FIG- URE 4 is made up of two concentrated winding portions 48 and 49 flanking a less concentrated uniformly distributed portion 51.

A damping ring 53 of copper or similar material of high electrical conductivity is also embedded in the molded cylinder 44. This ring is substantially co-extensive with the winding portion 51 so that eddy currents are induced in it as it moves through the air gap. The reactive force to the eddy currents tends to counterbalance the oppositely directed force exerted on the cylinder by the reaction of the air gap flux on the winding portion 51 to produce a viscous damping effect causing the cylinder velocity to level out at a desired value during exposure time.

Contact bars (FIGURE 2) 56 and 57 are embedded in the cylinder 44, each of which is connected to an end of the coil 45. Brushes 59 slidable in brush holders 61 ride respectively on the contact bars under the influence of pressure springs 63. The driving rod 20 is secured, as by cementing, to the end of the cylinder 44. The entire actuator 16 is enclosed by a two-part magnetic shield 66. The end of the cylinder 44 as it moves outwardly is protected by a cap 68 secured to the cylindrical member 35 in any suitable manner, as by screws 71. A guide 73 for the outer end of the driving rod 20 is mounted in the cap 68. Limits of travel of the cylinder 44 are fixed by a cushioning ring 74 which surrounds the guide 73 and a bumper cushion 75. To substantially eliminate bounce, the ring 74 and the cushion 75 are of elastomer material, silicone rubber for example. To aid in eliminating bounce, the time duration of application of current to the winding exceeds the time of travel of the actuator.

Operation of the shutter and actuator combination will now be described with reference to values of various factors given solely by way of example and for illustrative purposes. FIGURE 5 of the drawing is a velocity curve 78 for a shutter stroke of 0.97 inch. This curve is especially applicable to shutter travel in either direction. In the illustrative example, the exposure time is 1.2 milliseconds, this being the result of a stabilized shutter velocity of 50 inches per second with an aperture slit width of 0.060 inch since exposure time is equal to slit width in inches divided by shutter plate 23 velocity in inches per second. The exposure period indicated on FIGURE 5 is the time during which the slit 25 traverses the aperture 28. The curve 78 indicates a substantially constant high rate of initial acceleration produced by the coil portion 49 assuming that shutter travel is toward the right viewed in FIGURE 1. The substantially horizontal or constant velocity part of the curve is produced by the combined action of the coil portion 51 and damping ring 53. The curve 78 rises at its right hand end because of the coil portion 48 entering the air gap. Since the exposure is already complete this is immaterial. The coil portion 48 is in position for the next succeedng or return stroke and the velocity curve 78 also applies.

The actuator 16 and its associated shutter 18 may be driven by DC. (direct current) pulses which may be 22 milliseconds in duration. Successive pulses are reversed in polarity to accomplish shutter actuator motion reversal. Switching circuits of any known type may be used to time and produce these pulses.

What is claimed is:

1. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field, said coil comprising a winding portion adjacent one end thereof, said winding portion producing acceleration in one direction of said actuator from rest upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named winding portion, and conductive material retarding means on said coil, said second winding portion upon continued energization of said winding in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity as said second winding portion moves through said field.

2. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field, said coil comprising a Winding portion adjacent one end thereof, said winding portion producing acceleration in one direction of said actuator from rest upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named winding portion, and retarding means on said coil, said second winding portion upon continued energization of said winding in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity as said second winding portion moves through said field.

3. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field, said coil comprising a winding portion adjacent one end thereof, said winding portion producing acceleration in one direction of said actuator from rest upon energization of said winding by an electric current of one polarity as said winding portion moves through said field, a second winding portion next to said first named winding portion, conductive material retarding means on said coil, said second winding portion upon continued energization of said winding in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity as said second winding portion moves through said field, a third winding portion next to said second winding portion to produce acceleration of said actuator in a direction opposite the acceleration produced by said first portion upon energization of said winding by an electric current of opposite polarity as said third winding portion moves through said field.

4. An actuator for producing mechanical movement of a member comprising means including an exciting magnet and a pair of opposed pole pieces for producing a radial magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field, said coil comprising a winding portion adjacent one end thereof, said winding pontion producing acceleration in one direction of said actuator from rest upon energization of said winding by an electric current of one polarity as said winding portion moves through said field, a second winding portion next to said first named winding portion, conductive material retarding means on said coil, said second winding portion upon continued energization of said winding in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity as said second winding portion moves through said field, a third winding portion next to said second winding portion to produce acceleration of said actuator in a direction opposite the acceleration produced by said first portion upon energization of said winding by an electric current of opposite polarity as said third winding portion moves through said field.

5 An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field and comprising a winding portion adjacent one end thereof, said winding portion producing axial acceleration of said actuator upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named winding portion, retarding means on said coil coaxial with said second winding portion, said second winding portion in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity during continued energization as said second winding portion moves through said field, a third winding portion next to said winding portion to produce acceleration of said actuator in a direction opposite to the acceleration produced by said first portion upon energization of said winding by an electric current of opposite polarity as said third winding portion moves through said field.

6. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a self-supporting coil supported for axial movement through said field and comprising a winding portion of concentrated turns adjacent one end thereof, said winding portion producing axial acceleration of said actuator upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named winding portion, and a ring of conductive material on said coil coaxial with said second one portion, said second winding portion in conjunction with said ring producing continued movement of said actuator at substantially constant velocity during continued energization as said second Winding portion moves through said field.

7. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a self-supporting coil supported for axial movement through said field and comprising a winding portion of concentrated turns adjacent one end thereof, said winding portion producing axial acceleration of said actuator upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named winding portion, a ring of conductive material on said coil coaxial with said second winding portion, said second winding portion in conjunction with said ring producing continued movement of said actuator at substantially constant velocity during continued energization as said second winding portion moves through said field, a third winding portion of concentrated turns next to said second winding portion to produce acceleration of said actuator in a direction opposite to the acceleration produced by said first portion upon energization of said winding by an electric current of opposite polarity as said third winding portion moves through said field.

8. An actuator for producing mechanical movement of a member comprising means for producing a magnetic field of limited extent axially of said actuator, a coil supported for axial movement through said field, said coil comprising a winding portion adjacent one end thereof,

said Winding portion producing acceleration in one direction of said actuator from rest upon energization of said winding by an electric current as said winding portion moves through said field, a second winding portion next to said first named Winding portion, and conductive retarding means on said coil coaxial with and substantially coextensive axially of said second winding portion, said second winding portion upon continued energization of said winding in conjunction with said retarding means producing continued movement of said actuator at substantially constant velocity as said second winding portion moves through said field.

9. An actuator having an identical motion pattern in opposite directions on alternate strokes for producing mechanical movement of a member comprising a magnet structure having a magnetizable cylindrical member closed at one end thereof, said cylindrical member having a constricted portion at the opposite end thereof, a cylindrical permanent magnet coaxial with said cylindrical member secured to said closed end of said cylindrical member, a magnetizable pole piece secured to the free end of said permanent magnet and projecting into the restricted portion of said cylindrical member whereby to provide a cylindrical air gap across Which flux produced by said permanent magnet is concentrated, a movable coil structure axially slidable on said permanent magnet and said pole piece through said air gap, said coil structure comprising a molded cylindrical member having a coil embedded therein, said coil having two concentrated Winding portions flanking a less concentrated uniformly distributed portion, said Winding portions cooperating successively with said air gap upon axial movement of said molded member, a conductive damping ring embedded in said molded cylindrical member substantially coextensive with said uniformly distributed portion, and contact means on said molded member cooperating with stationary contact means projecting inwardly from said magnetizable cylindrical member to supply electric current to said coil.

References Cited by the Examiner UNITED STATES PATENTS 2,846,598 8/58 Zerisian 310-27 2,931,925 4/60 DOlZ 310-27 3,023,685 3/62 Meixner -5 3,049,982 8/62 Kendall -f/lifihi 9s ss e MILTON O. HIRSHFIELD, Primary Examiner.

DELBERT B. LOWE, Examiner. 

1. AN ACTUATOR FOR PRODUCING MECHANICAL MOVEMENT OF A MEMBER COMPRISING MEANS FOR PRODUCING A MAGNETIC FIELD OF LIMITED EXTENT AXIALLY OF SAID ACTUATOR, A COIL SUPPORTED FOR AXIAL MOVEMENT THROUGH SAID FIELD, SAID COIL COMPRISING A WINDING PORTION ADJACENT ONE END THEREOF, SAID WINDING PORTION PRODUCING ACCELERATION IN ONE DIRECTION OF SAID ACTUATOR FROM REST UPON ENERGIZATION OF SAID WINDING BY AN ELECTRIC CURRENT AS SAID WINDING PORTION MOVES THROUGH SAID FIELD, A SECOND WINDING PORTION NEXT TO SAID FIRST NAMED WINDING PORTION, AND CONDUCTIVE MATERIAL RETARDING MEANS ON SAID COIL, AND SECOND WINDING PORTION UPON CONTINUED ENERGIZATION OF SAID WINDING IN CONJUNCTION WITH SAID RETARDING MEANS PRODUCING CONTINUED MOVEMENT OF SAID ACTUATOR AT SUBSTANTIALLY CONSTANT VELOCITY AS SAID SECOND WINDING PORTION MOVES THROUGH SAID FIELD. 